Water shifts PdO-catalyzed lean methane combustion to Pt-catalyzed rich combustion in Pd-Pt catalysts: In situ X-ray absorption spectroscopy

- Pd-Pt catalysts are relatively insensitive to water poisoning in methane combustion.
- In situ spectroscopy shows a water-promoted increase of Pd(0)-to-oxidized Pd ratio.
- In situ study and thermodynamic analysis indicate a water-induced lack of oxygen.
- In the lack of oxygen, Pt(0) allows CH4 activation in Pd-Pt catalysts.
- PdO activates methane in dry combustion, and Pt(0) does so in the wet feed.

The addition of platinum to palladium is known to provide bimetallic catalysts that are relatively active in lean methane combustion in the presence of water at temperatures below 773 K, which is of practical interest for exhaust treatment from natural gas vehicles. The study provides insight into the wet lean methane combustion mechanism on the Pd-Pt/Al2O3 catalyst via in situ X-ray absorption spectroscopy studies at temperatures 473-873 K. The presence of water leads to an increased fraction of metallic Pd due to the lack of surface oxygen. The fraction of metallic Pd drops as the temperature increases. Oxygen deficit results in Pt atoms available for methane dissociation, which does not occur in the dry methane-lean feed, in which oxygen poisons Pt.

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